The present invention relates to flight instrumentation for aircraft. More particularly, it relates to a measurement, data manipulation and information display system and method for use on air vehicles, wherein the system includes pressure sensors, a data processor, at least one data port for electrically exporting angles from zero lift, and an indicator for communicating information relating to angles from zero lift.
Past and present pressure type angle of attack devices use a variety of differently shaped probes. A hemispherical end sensor is described in U.S. Pat. No. 3,318,146. Angle of attack (AOA) and angle of side slip both are calculated from the pressure signals present at five ports on the end. This angle of attack measuring device requires use of the probe as described and the probe must be installed at a very precise angle relative to the cord of the wing or some other longitudinal plane of the air machine.
Sharp tipped pitot static tubes with angle of attack sensing ports are shown in U.S. Pat. Nos. 4,096,744 and 4,378,696. These patents show probes providing differential pressures which are used for determining angle of attack. In the '696 patent, a combination of differential pressure at two ports on the probe, measured pitot and static pressure is used. In the '744 patent, measured pitot pressure, pressure at one of the angle of attack sensitive ports and measured impact pressure are utilized for the calculations.
U.S. Pat. No. 5,616,861 discloses a plurality of air sensing probes symmetrically mounted on opposite sides of a vertical center plane of the air vehicle which includes the longitudinal axis of the air vehicle.
In each of the above instances, the angle of attack systems require special probes usually installed at very precise angles relative to the cord of the airfoil, each other, or other longitudinal axis of the air vehicle.
Additionally, in the above instances and other known sensor systems, the probes must be located well ahead of the wing to reduce the effect of changes in lift and configuration. Usually the probe is located on or near the nose of an aircraft. This is a problem since many factors can affect the relationship between the local AOA and the true wing AOA. The airflow around the nose is not the same as that at the wing. Pitch rate errors occur when the nose of an aircraft is pitched up or down causing the probe to indicate too high or too low. In a turn, for example, the nose is pitched up reducing the local flow angle and causing the AOA reading to be too low. Because of the shape of the nose, sensitivity errors are introduced. A one degree change in true wing AOA may cause the local flow angle at the nose to be 1.5 to 2 degrees.
Another problem with systems such as those noted above is that the measurement used was based on angle of attack which is the angle between the cord of the airfoil and the relative wind. The above patented devices are representative of the many devices that have been invented and installed on aircraft to produce a known pressure differential at a known angle of attack. Typically, they require that a probe or probes be installed at a fixed angle relative to a known plane of the air vehicle, usually the cord or surface of the wing or longitudinal axis of the air vehicle.
In recent years, there has been emphasis on making pressure sensing probes compact, light and with low drag as illustrated by the devices shown in U.S. Pat. Nos. 4,836,019, 5,616,861 and 5,331,849. However, there is still room for improvement.
U.S. Pat. No. 4,350,314 describes a stall condition detector that uses four pressure ports in the wing which are ported to a capacitance device within the wing. The detector involves four electrically conductive hollow tubes with rods extending up through the tubes. The tubes are filled with a dielectric fluid. Devices of this type may be subject to errors induced by temperature and other forces acting upon the dielectric fluids resulting from turbulence, G loads, slips and skids. Additionally, with the emphasis of higher loaded airfoils, the newer airfoil designs are smaller and thinner, thus having smaller interior compartments, making these devices difficult to install. In addition, the angle of attack display of this type of device does not take into account high lift devices which may significantly reconfigure the shape of the airfoil.
An aircraft instrument system for communicating accurate information involving angles from zero lift, wherein the information may be derived from simple pressure ports rather than known probes or detectors of the type disclosed in the '314 patent, would be advantageous.